A small displacement engine may be boosted (e.g., pressurizing) to provide power output that is similar to a larger engine. The smaller engine may exhibit reduced pumping losses and reduced engine friction as compared to a larger engine. However, it may be more difficult for the smaller engine to produce a same amount of intake manifold vacuum as the larger engine when both the smaller engine and the larger engine are operating at a same speed and torque output. Further, the smaller engine may provide sufficient vacuum for vehicle vacuum systems during some conditions, but the same engine may not provide sufficient vacuum for vehicle vacuum systems during other conditions. Consequently, it may be desirable to provide a way for smaller displacement engines to provide sufficient levels of intake manifold vacuum during a broader range of engine operating conditions.
The inventors herein have recognized the above-mentioned issues and have developed a vehicle method, comprising: shifting a transmission from a gear to neutral via a controller in response to an actual total number of braking events being greater than a threshold.
By shifting a transmission coupled to an engine into neutral from a forward or reverse gear, load on the engine may be reduced so that engine intake manifold pressure may be reduced. The engine may provide additional vacuum to vehicle vacuum systems when intake manifold pressure is lower. For example, shifting the transmission into neutral may alleviate one particular condition where the smaller engine may have difficulty providing a desired amount of vacuum at higher altitudes. In particular, during a condition where a driver repeatedly applies and partially releases a brake pedal when a vehicle is stopped at a higher altitude, shifting the transmission into neutral may increase engine vacuum and reduce a possibility of hard brake pedal feel.
The present description may provide several advantages. Specifically, the approach may improve operation of a vehicle's vacuum operated systems. Additionally, the approach may not increase engine fuel consumption much of the time since the approach may only be applied during selected engine operating conditions that may not be frequently encountered. Further, the approach may improve driver satisfaction by reducing the possibility of hard brake pedal feel. Shifting the transmission to neutral results in a slightly delayed acceleration upon commanding vehicle acceleration with the accelerator pedal if the transmission engagement torque application is managed. Thus, neutral idle may be used to improve brake booster vacuum only during select conditions where vacuum production is desired to reduce the possibility of low vacuum conditions. This action may be applied at high altitude (low BP) and closely repeated brake pedal motion conditions. The method detects these conditions and commands neutral idle when they occur. Further, neutral idle is also commanded when brake booster vacuum is below a threshold.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.